1. Field of the Invention
This invention relates to an electrostatic copying apparatus and an auxiliary unit to be mounted detachably on it. More specifically, this invention pertains to an electrostatic copying apparatus and an auxiliary unit which is detachably mounted on it and can diversify the mode of forming a copied image.
2. Description of the Prior Art
As is well known to those skilled in the art, "multimode" electrostatic copying apparatuses have recently been proposed and come into commercial acceptance which can selectively perform an ordinary copying mode (the mode whereby a copied image of a single document is formed on one surface of a copying paper), and a both surface copying mode (the mode whereby a copied image of a document is formed on one surface of a copying paper and then a copied image of another document is formed on the other surface of the paper) and/or an overlapping copying mode (the mode whereby a copied image of a document is formed on one surface of a copying paper and then a copied image of another document is overlappingly formed on the aforesaid one surface of the paper).
Conventional multimode electrostatic copying apparatuses, however, have various problems to be solved. The conventional multimode electrostatic copying apparatuses are equipped with various elements for selectively performing the both surface copying mode and/or the overlapping copying mode in addition to the ordinary copying mode as parts essential to the apparatus itself. In the electrostatic copying apparatus market, there is a first demand for multimode electrostatic copying apparatuses which can selectively perform the both surface copying mode and/or the overlapping copying mode in addition to the ordinary copying mode and are relatively expensive, and there is also a second demand for "single mode" electrostatic copying apparatuses which can perform the ordinary copying mode and are relatively inexpensive. The conventional multimode electrostatic copying apparatuses can meet the first demand but cannot meet the second demand. The manufacturers and sellers, therefore, should manufacture and sell the single mode electrostatic copying apparatuses meeting the second demand separately from the multimode apparatuses. This complicates a control of manufacture and stock of apparatuses and entails an increase in cost. The consumer initially purchases a single mode electrostatic copying apparatus with which he is fully satisfied, but when a need arises later to perform the both surface copying mode and/or the overlapping copying mode, he must purchase a multimode electrostatic copying apparatus. In such a case, the previously purchased single mode electrostatic apparatus becomes a waste.
In view of this fact, U.S. patent application Ser. No. 650,605 now U.S. Pat. No. 4,607,942 whose assignee is the same as the assignee of the present application, or the corresponding European Patent Application No. 84111120.6 proposed an auxiliary unit which can be detachably mounted as desired on a relatively inexpensive electrostatic copying apparatus capable of performing only the ordinary copying mode, and which selectively performs the ordinary copying mode or the both surface copying mode. The previously proposed auxiliary unit, however, has not proved to be entirely satisfactory and entails problems that have to be solved. Among these problems are:
(a) It is relatively complex and expensive.
(b) It is relatively bulky.
(c) It can peform the both surface copying mode selectively in addition to the ordinary copying mode, but cannot perform the overlapping copying mode.
(d) There is a great likelihood that a trouble will occur in conveying a copying paper within the auxiliary unit to cause paper jamming.
(e) In the event of papeCr jamming, the operation of removing the paper is comparatively difficult.
(f) The widthwise position of a copying paper in the auxiliary unit can be regulated only insufficiently, and a copied image cannot be formed in a required manner on the other surface of a copying paper in the both surface copying mode.